I might agree with you if it weren’t for the fact that state Supreme Courts that have ruled against retroactive aspects of the SOR laws in many states. In PA, for example, The PA Supreme Court’s ruling against SORNA led the state to change it’s law to apply to “AN INDIVIDUAL WHO, ON OR AFTER THE EFFECTIVE DATE” to register. That effective date is December 12, 2012. If you have not been convicted of, or are incarcerated or on a form of supervised release for a crime requiring registration after that date, the law can not be applied retroactively to you. The caveat is, you would have had to complete a period of registration prior to the effective date [and you get credit for registration on ANY registry in the United States (Jackson v. Commonwealth)].
As I stated above, Gorsuch might be key in ruling against retroactive application of SORNA, at the very least. In United States v. Nichols he dissented and objected to how much regulatory power a federal statute [SORNA] gave to the Justice Department to apply its rules to those guilty of sex crimes predating the act’s enactment.